CAUSES OF VARIATION 135 



which we can generally recognise as resembling the 

 action of intelligence. In fact, we know from the 

 phenomena of memory that it does originate changes 

 in the brain. Mind is the "vital force" which 

 so many physiologists now believe in. But the 

 essence of mind is thought ; and psychogenesis must 

 be due to a form of thought thought of the cell- 

 mind. 



There is one general argument that may be urged 

 in favour of psychogenesis. It seems- probable that 

 the energy of inheritance must have been slight in 

 the early organisms, and that it increased with 

 repetition ; for this is the teaching of a large number 

 of experiments and observations on new varieties. 

 But we learn from palaeontology that variation was 

 slow at first, and that it became more rapid as the 

 world grew older, so that the cause of variation 

 must have increased in intensity. Now the most 

 reasonable hypothesis appears to be that the rate of 

 variation increased as animals got more intelligent. 

 So that the rate of variation depends largely on the 

 intelligence of the animal or plant. This is indirect 

 evidence of psychogenesis. 



